A conventional multigroup, multiphase driving system includes a power converter that converts direct current power into alternating current power and vice versa, a direct current power supply connected to a direct current side of the power converter so as to be charged with and discharge direct current power, and a rotary electric machine that is connected to an alternating current side of the power converter and includes a plurality of groups of multiphase armature windings. When a load exerted on the multigroup, multiphase driving system is large, the rotary electric machine is driven using all of the groups, and when the load is small, the rotary electric machine is driven using only some of the groups. As a result, an improvement in efficiency is achieved at a low load (see PTL 1, for example).